The invention relates to a method for providing a signal output and to a vehicle.
Therefore, an apparatus linked to a data network is what caters for the signal output. A main file names at least one secondary file, and at least one secondary file determines a signal output. The main file and the at least one secondary file can be obtained (downloaded) by the apparatus via the data network.
Such a method is known from use of the internet (World Wide Web). In this case, the main file is available as an HTML document, for example, which specifies the basic framework for a graphical representation, and the secondary files represent individual images or icons to be incorporated into the graphical representation. The secondary files may also be video or audio files or the like.
The internet can be used in a vehicle particularly for what is known as “Remote HMI”, remote human-machine interface. This involves extending the functionalities of the operator control apparatus of the vehicle (what is known as the infotainment system) retrospectively. However, this is complex because a large number of secondary files need to be loaded from the internet. The download of these secondary files gives rise to not inconsiderable costs for the data traffic. Furthermore, the download of such secondary files from the internet in a traveling vehicle can frequently cause interruptions and delays. As is usually known from the use of the internet, it is possible to make do with buffer-storing the secondary files in a memory in the vehicle. However, in this case the problem arises that a secondary file can also change: the infotainment therefore has to establish when it needs to replace a buffer-stored secondary file with a new version provided by the server of the manufacturer. In this case, it is a popular approach for the server of the manufacturer to use fields in the control protocol to denote whether a requested secondary file has changed. In the http (Hypertext Transfer Protocol) protocol, this is accomplished by using the http headers “ETag”, “Modified-Since”, “If-Modified-Since” and “If-None-Match”, for example. A drawback in this case is that the infotainment system has to individually check with the server of the manufacturer, for each secondary file, whether said secondary file has changed. The signal output cannot take place until after an individual check has been performed for each of the secondary files to determine whether said secondary file has been modified. Added to this is that there is not always a reliable system time in the vehicle, which makes it difficult to use time-oriented mechanisms for updating the buffer store.
U.S. 2005/0131900 A1 describes a method for obtaining data from a network. The resources that are present on a client server are stored together with the hash values therefor in a memory. In this case, the client server may also be part of a local area network with a pool server, the memory of which stores copies of all the resources that are present in the local area network together with their associated hash values. The local area network may be coupled to a larger network, e.g. the World Wide Web. When a client requests a resource, the hash value associated with the requested resource is first of all transmitted to the client, and it is compared with the hash values stored in the memory of the client or that of the pool server. If this establishes that the requested resource is present in the proprietary memory or in the local area network, the requested resource is obtained via the local area network, otherwise the resource is downloaded from the larger network.
KELLY T: “Thin-client Web access patterns: Measurements form a cache-busting proxy”, COMPUTER COMMUNICATIONS, ELSEVIER SCIENCE PUBLISHERS BV, AMSTERDAM, NL, vol. 25, No. 4, Mar. 1, 2002, pages 357-366, discloses a method for preventing redundant data transmission from a proxy server to a client. In this case, the browser stores all the received data without exception and makes habitual requests to the proxy server, and, before the proxy server transmits the requested data to the client, a checksum for the relevant data is first of all transmitted that the browser compares with the checksums for the stored data.